Insulin resistance and increased oxidants are characteristics of endothelial cells exposed to a variety of cardiovascular risk factors that contribute to atherosclerosis. The principal hypothesis of this proposal is that oxidants that arise in endothelial cells are themselves responsible for interfering with normal insulin signaling that maintains normal endothelial function. Preliminary studies indicate that exposure of endothelial cells to peroxynitrite (ONOO-) or oxidized LDL interrupts insulin-mediated signaling via PIS kinase and Akt, which normally phosphorylates and stimulates NO release from endothelial nitric oxide synthase (eNOS). The purpose of the proposed studies is to investigate the molecular mechanism of this phenomenon and its consequences with respect to aortic endothelial dysfunction and atherosclerosis. Endothelium-derived oxidants exert specific effects on cell signaling. Our preliminary studies indicate that ONOO- reacts with redox-sensitive thiols on the small GTPase, Ras, thereby activating the protein and initiating downstream signaling in cultured bovine aortic endothelial cells (BAEC). We propose to study these novel redox-dependent effects on Ras and its role in mediating insulin resistance and endothelial dysfunction. We will use proteomic methods to determine the mechanisms by which oxidants influence Ras activity, and also to screen for oxidant changes in other signaling elements that participate in insulin signaling. The significance of oxidant-mediated endothelial insulin resistance in impaired NOS activity, endothelial inflammation, and atherogenesis will be examined in insulin-resistant low density lipoprotein deficient (LDLr -/-) mice fed a high fat, high sucrose (HFHS) diet, and in transgenic mice with conditional endothelial cell specific expression of a Ras dominant-negative, a constitutively active Ras, as well as a constitutively active Akt mutant protein. These studies will elucidate the mechanism by which oxidants impair insulin signaling and determine the importance of impaired signaling to Akt for decreased NO production by eNOS and increased atherogenesis.